The present invention relates to a thermally processed image recording material. In particular, the present invention relates to a thermally processed image recording material that shows superior image storability after heat development.
There are known many photosensitive materials having a photosensitive layer on a support, with which image formation is attained by imagewise light exposure. Those materials include those utilizing a technique of forming images by heat treatment as systems that can contribute to the environmental protection and simplification of image forming means.
In recent years, reduction of amount of waste processing solutions is strongly desired in the field of films for medical use and the field of photographic art films from the standpoints of environmental protection and space savings. Therefore, development of techniques relating to thermally processed image recording materials for medical diagnosis films and photographic art films are required, which materials enables efficient exposure by a laser image setter or laser imager and formation of a clear black image having high resolution and sharpness. Such thermally processed image recording materials can provide users with a simple and non-polluting heat development processing system that eliminates the use of solution-type processing chemicals.
Among such thermally processed image recording materials, those materials for medical images are required to provide high quality of images excellent in sharpness and graininess, since such images are required to be very fine images. In addition, for easy diagnosis, cold monochromatic images are preferred. At present, various types of hard copy systems using pigments and dyes, for example, ink jet printers and electrophotographic systems, are available as ordinary imaging systems. However, no satisfactory image-forming system is available for medical images.
Methods for forming images by heat development are described in, for example, U.S. Pat. Nos. 3,152,904 and 3,457,075 and Klostervoer, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d, Imaging Processes and Materials, Neblette, 8th ed., compiled by J. Sturge, V. Walworth and A. Shepp, Chapter 9, p. 279, (1989). Such photothermographic materials comprise a reducible non-photosensitive silver salt (e.g., silver salt of an organic acid), a photocatalyst (e.g., silver halide) in a catalytically active amount and a reducing agent for silver, which are usually dispersed in an organic binder matrix. While the photosensitive materials are stable at an ordinary temperature, when they are heated to a high temperature (e.g., 80xc2x0 C. or higher) after light exposure, silver is produced through an oxidation-reduction reaction between the reducible silver salt (which functions as an oxidizing agent) and the reducing agent. The oxidation-reduction reaction is accelerated by catalytic action of a latent image of silver halide generated upon exposure. The silver resulted from the reaction of the reducible silver salt in the exposed areas shows black color that provides contrast with respect to the non-exposed areas, and thus images are formed. Thermally processed image recording materials and systems therefor based on the above principle are disclosed in many references including U.S. Pat. No. 2,910,377 and Japanese Patent Publication (Kokoku, hereinafter referred to as JP-B) 43-4924.
However, since such thermally processed image recording materials are not subjected to a fixation treatment after the heat development, they suffer from a problem that the silver salt of an organic acid, and possibly a photosensitive silver halide, when the materials are photothermographic materials, are left as they are in the materials even after the heat development, and thus white portions are colored when the materials are left at a high temperature for a long period of time after the heat development.
Therefore, an object of the present invention is to provide a thermally processed image recording material that shows improved image storability after the heat development, i.e., that shows improved coloration of white portions observed when the material is left at a high temperature. Another object of the present invention is to provide a thermally processed image recording material that comprises a transparent layer showing low haze and superior brittleness.
The inventors of the present invention assiduously studied in order to achieve the aforementioned objects. As a result, they found that an excellent thermally processed image recording material that provides the desired effects could be obtained by using a dispersion of polymer microparticles having a core/shell structure which satisfies particular requirements as a binder, and thus accomplished the present invention.
That is, the present invention provides a thermally processed image recording material having an image-forming layer that contains a non-photosensitive silver salt of an organic acid, a reducing agent for silver ions and a binder on a support, wherein the binder is coated as a dispersion of polymer microparticles having a core/shell structure, glass transition temperature of shell part of the core/shell structure is higher than glass transition temperature of core part, and the binder shows a minimum film-forming temperature of 30xc2x0 C. or lower.
The glass transition temperature of the core part of the core/shell structure is preferably 10xc2x0 C. or lower, and the glass transition temperature of the shell part is preferably 40xc2x0 C. or higher. Further, the dispersion of polymer microparticles is preferably latex prepared by emulsion polymerization. Furthermore, the image-forming layer preferably contains a photosensitive silver halide.
According to the present invention, there can be provided thermally processed image recording materials that provide improved image storability after heat development, i.e., improved coloration of white portions when the materials are left at a high temperature, and have transparent coated films with low haze that are also excellent in brittleness.
The present invention will be explained in detail hereafter.
The thermally processed image recording material of the present invention has an image-forming layer that contains a non-photosensitive silver salt of an organic acid, a reducing agent for silver ions and a binder on a support. The aforementioned image-forming layer preferably further contains a photosensitive silver halide. In this case, the image-forming layer is a photosensitive layer, and the thermally processed image recording material of the present invention includes a photothermographic material.
The binder used for the image-forming layer of the thermally processed image recording material of the present invention is characterized in that it is provided by coating a dispersion of polymer microparticles that have a core/shell structure, the glass transition temperature of the shell part of the core/shell structure is higher than that of the core part, and the minimum film forming temperature of the binder is 30xc2x0 C. or lower. The image-forming layer is preferably formed by coating and drying the coating solution which is prepared by mixing a dispersion of the aforementioned polymer microparticles with other ingredients.
The binder of the image-forming layer serves as a field of the image formation by the heat development, and provides a storage environment for the picture elements during image storage. The aging stability of the images formed by the development is greatly affected by the environment surrounding the silver grains that can be picture elements. Thermally processed materials, in particular, do not undergo a fixation reaction process as described above, and therefore non-imagewise development may occur even after the image formation. In the thermally processed materials, in general, significant improvement in storage stability can be obtained by reducing diffusibility of the compounds involved in the development process which present around the developable silver grains that can form picture elements under the storage condition. That is, by increasing the glass transition temperature (also referred to as Tg hereinafter) of the binder being in contact with the image silver grains, the motility of low molecular weight compounds is reduced and thus improvement of the image storability can be attained. On the other hand, when Tg is increased, the binder system usually suffers from a problem that the film-forming temperature (minimum film forming temperature: hereinafter also abbreviated as MFT) is elevated due to the increase of Tg, and thus sufficient film-forming property can no longer be obtained. The technical characteristic of the binder of the image-forming layer of the present invention is that higher Tg of the polymer field contacting with the silver images and impartation of film-forming property obtained by the deformation of particles can be simultaneously obtained by elevating Tg of particle surfaces and lowering Tg of the inside of the particles.
The binder of the image-forming layer is provided by coating a dispersion of polymer microparticles having a core/shell structure, and the glass transition temperature of the shell part of the core/shell structure is higher than that of the core part. That is, the dispersion consists of soft core/hard shell latex (also abbreviated as xe2x80x9cSC-HS latexxe2x80x9d hereinafter). The difference of the glass transition temperature of the core part and the glass transition temperature of the shell part is preferably 30-130xc2x0 C., more preferably 55-100xc2x0 C. In the present specification, the range indicated with xe2x80x9c-xe2x80x9d means a range including the numerical values before and after xe2x80x9c-xe2x80x9d as the minimum and maximum values.
The glass transition temperature of the core part is preferably 10xc2x0 C. or lower, more preferably xe2x88x9230-10xc2x0 C., further preferably xe2x88x9220-5xc2x0 C., in view of film-forming property, brittleness and so forth. The glass transition temperature of the shell part is preferably 40xc2x0 C. or higher, more preferably 50-100xc2x0 C., further preferably 60-80xc2x0 C., in view of image storability.
Monomers that can be used as raw materials of the polymers for the core part and the shell part are not particularly limited, and those polymerizable by ordinary radical polymerization or ion polymerization can suitably be used. Preferably, the polymers of the core part and the shell part are homopolymers or copolymers of monomers arbitrarily selected from the monomers mentioned below so that the aforementioned relationship of the glass transition temperatures of the core part and the shell part could be satisfied.
Monomers
(a) Olefins: ethylene, propylene, isoprene, butadiene, pentadiene, cyclopentadiene, vinyl chloride, vinylidene chloride, 6-hydroxy-1-hexene, 4-pentenoic acid, methyl 8-nonenoate, vinyl sulfonate, trimethylvinylsilane, trimethoxyvinylsilane, 1,4-divinylcyelohexane, 1,2,5-trivinylcyelohexane etc.;
(b) xcex1- and xcex2-unsaturated carboxylic acids and salts thereof: acrylic acid, methacrylic acid, itaconic acid, maleic acid, sodium acrylate, ammonium methacrylate, potassium itaconate etc.;
(c) derivatives of xcex1- and xcex2-unsaturated carboxylic acids: alkyl acrylates (for example, methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate etc.), substituted alkyl acrylates (for example, 2-chloroethyl acrylate, benzyl acrylate, 2-cyanoethyl acrylate etc.), alkyl methacrylates (for example, methyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate etc.), substituted alkyl methacrylates (for example, 2-hydroxyethyl methacrylate, glycidyl methacrylate, glycerol monomethacrylate, 2-acetoxyethyl methacrylate, tetrahydrofurfuryl methacrylate, 2-methoxyethyl methacrylate, xcfx89-methoxypolyethylene glycol methacrylate (added molar number=2-100), polyethylene glycol monomethacrylate (added molar number of polyoxyethylene=2-100), polypropylene glycol monomethacrylate (added molar number of polyoxypropylene=2-100), 3-N,N-dimethylamino-propyl methacrylate, chloro-3-N,N,N-trimethylammoniopropyl methacrylate, 2-carboxyethyl methacrylate, 3-sulfopropyl methacrylate, 4-oxysulfobutyl methacrylate, 3-trimethoxy-silylpropyl methacrylate, allyl methacrylate, 2-isocyanatoethyl methacrylate etc.), derivatives of unsaturated dicarboxylic acids (for example, monobutyl maleate, dimethyl maleate, monomethyl itaconate, dibutyl itaconate etc.), polyfunctional esters (for example, ethylene glycol diacrylate, ethylene glycol dimethacyrlate, 1,4-cyelohexane diacrylate, pentaerythritol tetramethacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, trimethylolethane triacrylate, dipentaerythritol pentamethacrylate, pentaerythritol hexaacrylate, 1,2,4-cyelohexane tetramethacrylate etc.);
(d) amides of xcex2-unsaturated carboxylic acids: acrylamide, methacrylamide, N-methylacrylamide, N,N-dimethylacrylamide, N-methyl-N-hydroxyethylmethacrylamide, N-tert-butylacryl-amide, N-tert-octylmethacrylamide, N-cyclohexylacrylamide, N-phenylacrylamide, N-(2-acetoacetoxyethyl)acrylamide, N-acryloylmorpholine, diacetone acrylamide, itaconic acid diamide, N-methylmaleimide, 2-acrylamido-2-methylpropane-sulfonic acid, methylene bisacrylamide, dimethacryloylpiperazine etc.;
(e) unsaturated nitriles: acrylonitrile, methacrylonitrile, etc.;
(f) styrene and derivatives thereof: styrene, vinyltoluene, p-tert-butylstyrene, vinyl benzoate, vinyl methylbenzoate, xcex1-methylstyrene, p-chloromethylstyrene, vinylnaphthalene, p-hydroxymethylstyrene, p-styrenesulfonic acid sodium salt, p-styrenesulfinic acid potassium salt, p-aminomethylstyrene, 1,4-divinylbenzene, 4-vinylbenzoic acid 2-acryloylethyl ester etc.;
(g) vinyl ethers: methyl vinyl ether, butyl vinyl ether, methoxyethyl vinyl ether etc.
(h) vinyl esters: vinyl acetate, vinyl propionate, vinyl benzoate, vinyl salicylate, vinyl chloroacetate etc.;
(i) other polymerizable monomers: N-vinylimidazole, 4-vinylpyridine, N-vinylpyrrolidone, 2-vinyloxazoline, 2-isopropenyloxazoline, divinylsulfone etc.
Preferably, the polymers of the core part and the shell part mainly consist of homopolymers or copolymers of acryl and methacryl resins, styrene resins, conjugated diene resins, vinyl chloride resins, vinyl acetate resins, vinylidene chloride resins, polyolefin resins and so forth. Among these, particularly preferred are homopolymers or copolymers containing one or more kinds of conjugated dienes (for example, isoprene, butadiene etc.) as the constitutive monomers.
Although the weight ratio of the core part and the shell part in the binder of the image-forming layer is not particularly limited, the weight ratio of the core part accounts for usually 10-90 weight %, preferably 20-80 weight %, more preferably 30-70 weight %.
The minimum film-forming temperature of the binder of the image-forming layer is 30xc2x0 C. or lower, preferably xe2x88x9250-20xc2x0 C., more preferably xe2x88x9220-15xc2x0 C.
Preferred examples of polymers of the core part and the shell part for the binder of the image-forming layer are mentioned in Table 1 below. However, the present invention is not limited to these.
The numerals used herein for the composition ratios of the monomers and the core/shell ratios indicate weight percents, and molecular weights indicate number average molecular weights, unless otherwise indicated. As for the cases where a polyfunctional monomer is used, description is omitted because the concept of molecular weight is not applicable. Glass transition temperature is indicated as Tg.
Tg was calculated according to the following equation.
1/Tg=xcexa3(Xi/Tgi) 
In the equation, it is assumed that a polymer consists of n of copolymerized monomers. Xi represents a weight ratio of i-th monomer (xcexa3xi=1), and Tgi represents glass transition temperature (absolute temperature) of a homopolymer of the i-th monomer. xcexa3 means the sum of from i=1 to n. As the values of glass transition temperature of homopolymers (Tgi), employed are those mentioned in J. Brandrup and E. H. Immergut, Polymer Handbook (3rd Edition), Wiley-Interscience (1989)).
The minimum film-forming temperature (MFT) was measured by using a film-forming temperature measurement apparatus (MFT-1) produced by Yoshimitsu Seiki.
These polymers may be used by each alone, or two or more of them may be used in combination as reqired. It is also possible to use the above polymers together with other polymers.
The method for producing the dispersion of polymer microparticles having a core/shell structure, which is the binder of the image-forming layer, is not particularly limited so long as the method is one that can be used for the production of photographic materials.
The dispersion of polymer microparticles having a core/shell structure is preferably an aqueous dispersion, and examples thereof include xe2x80x9cpolymer emulsionxe2x80x9d, which is obtained by emulsion dispersion of a polymer solution in a water-immiscible solvent (e.g., ethyl acetate, perfluoroalkanes etc.) in an aqueous medium in the presence of surfactant, protective colloid or the like, xe2x80x9cpolymer latexxe2x80x9d, which is obtained by direct dispersion of polymer in an aqueous medium during the production of the polymer, and so forth. In particular, the latter latex is preferred as the dispersion of polymer microparticles having a core/shell structure used for the present invention, because it enables formation of fine microparticles, shows good dispersion stability, and requires less amount of surfactant used together. The particle size of the microparticles in the latex is usually 500 nm or less, preferably 300 nm or less, more preferably 200 nm or less.
Latex preferably used as the dispersion of polymer microparticles having a core/shell structure can be obtained by usual polymerization reactions such as emulsion polymerization, dispersion polymerization and suspension polymerization. However, in most cases, coating of photographic photosensitive materials is performed by using water as a medium, and non-water-soluble substances such as the aforementioned polymers are used in the form of aqueous dispersion. Therefore, in view of preparation of coating solution, emulsion polymerization or dispersion polymerization is preferred, and it is particularly preferably prepared by emulsion polymerization.
Emulsion polymerization can be performed by using water or a mixed solvent consisting of water and a water-miscible organic solvent (for example, methanol, ethanol, acetone etc.) as a dispersion medium, and allowing polymerization of monomer mixture in an amount of 5-40 weight % with respect to the dispersion medium at 30-100xc2x0 C., preferably at 60-90xc2x0 C., for 3 to 8 hours with stirring in the presence of a polymerization initiator and emulsifier in amounts of 0.05-5 weight % and 0.1-20 weight %, respectively, with respect to the monomers. Conditions including dispersion medium, concentrations of monomers, amount of initiator, amount of emulsifier, reaction temperature, time, addition methods of monomers and so forth can be optionally selected by considering the types of monomers to be used, intended particle size of the microparticles and so forth.
Examples of polymerization initiators preferably used for emulsion polymerization include inorganic peroxides such as potassium persulfate and ammonium persulfate, azonitrile compounds such as sodium salt of azobiscyanovaleric acid, azoamidine compounds such as 2,2xe2x80x2-azobis(2-amidinopropane) dihydrochloride, cyclic azoamidine compounds such as 2,2xe2x80x2-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] hydrochloride, azoamide compounds such as 2,2xe2x80x2-azobis{2-methyl-N-[1,1xe2x80x2-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}. Among these, potassium persulfate and ammonium persulfate are particularly preferred.
As the emulsifier, although any of anionic surfactants, nonionic surfactants, cationic surfactants and amphoteric surfactants can be used, anionic surfactants are preferred.
Latex preferably used as the dispersion of polymer microparticles having a core/shell structure can be readily prepared by usual procedure of emulsion polymerization. General procedures of emulsion polymerization are detailed in the following literature: xe2x80x9cGosei Jushi Emulsion (Synthetic Resin Emulsion)xe2x80x9d, compiled by Taira Okuda and Hiroshi Inagaki, issued by Kobunshi Kanko Kai (1978); xe2x80x9cGosei Latex no Oyo (Application of Synthetic Latex)xe2x80x9d, compiled by Takaaki Sugimura, Yasuo Kataoka, Souichi Suzuki and Keishi Kasahara, issued by Kobunshi Kanko Kai (1993); and Soichi Muroi, xe2x80x9cGosei Latex no Kagaku (Chemistry of Synthetic Latex)xe2x80x9d, Kobunshi Kanko Kai (1970).
The latex preferably used for the present invention may be of any type so long as it is a dispersion of polymer microparticles. The dispersed state may be emulsion dispersion, micelle dispersion, dispersion in which polymer molecules having a hydrophilic portion are dispersed in molecular state or the like. Among these, polymer dispersion prepared by emulsion polymerization is preferred.
As the organic solvent that can be used together with the medium of the polymer microparticle dispersion, water-miscible organic solvents are preferred. Examples thereof include, for example, alcohols such as methyl alcohol, ethyl alcohol and propyl alcohol, cellosolves such as methyl cellosolve, ethyl cellosolve and butyl cellosolve, ethyl acetate, dimethylformamide and so forth. The content of these solvents is preferably 50 weight % or less, more preferably 30 weight % or less, with respect to water. Preferred examples of the solvent composition are water alone, water/methyl alcohol =90/10, water/methyl alcohol=70/30, water/methyl alcohol/dimethylformamide=80/15/5, water/methyl alcohol/ethyl cellosolve=85/10/5, water/methyl alcohol/isopropyl alcohol=85/10/5 and so forth (numerals indicate weight %).
The equilibrated moisture content of the binder polymer used for the present invention at 25xc2x0 C. and relative humidity of 60% is preferably 2 weight % or less, more preferably 0.01-1.5 weight %, further preferably 0.02-1 weight %.
The xe2x80x9cequilibrated moisture content at 25xc2x0 C. and relative humidity of 60%xe2x80x9d referred to herein is represented by the following equation, in which W1 indicates the weight of a polymer in humidity-conditioned equilibrium at 25xc2x0 C. and relative humidity of 60%, and W0 indicates the absolute dry weight of the polymer at 25xc2x0 C. Equilibrated moisture content at 25xc2x0 C. and relative humidity of 60%=[(W1xe2x88x92W0)/W0]xc3x97100 (weight %)
For the details of the definition of moisture content and the method for measuring it, for example, Lecture of Polymer Engineering, 14, Test Methods for Polymer Materials (Polymer Society of Japan, Chijin Shokan) can be referred to.
In the present invention, the amount of the binder in the image-forming layer is preferably 0.2 to 30 g/m2, more preferably 1 to 15 g/m2. The weight ratio of total binder/organic silver salt is preferably 1/10-10/1, more preferably 1/5-4/1.
Such an image-forming layer is preferably also a photosensitive layer (emulsion layer) containing a photosensitive silver halide, which is a photosensitive silver salt. In such a case, the weight ratio of total binder/silver halide is preferably 400-5, more preferably 200-14 10. 
The non-photosensitive silver salt of an organic acid used in the present invention is a silver salt relatively stable against light, but forms a silver image when it is heated at 80xc2x0 C. or higher in the presence of an exposed photocatalyst (e.g., a latent image of photosensitive silver halide) and a reducing agent. The silver salt of an organic acid may be any organic substance containing a source of reducible silver ions. Such non-photosensitive silver salts of an organic acid are disclosed in Japanese Patent Laid-open Publication (Kokai, hereinafter referred to as JP-A) 10-62899, paragraphs 0048 to 0049, EP0803763A1, page 18, line 24 to page 19, line 37, and EP962812A1. Silver salts of an organic acid, in particular, silver salts of a long chained aliphatic carboxylic acid having from 10 to 30, preferably from 15 to 28 carbon atoms, are preferred. Preferred examples of the silver salt of an organic acid include silver behenate, silver arachidinate, silver stearate, silver oleate, silver laurate, silver caproate, silver myristate, silver palmitate, mixtures thereof and so forth.
While the silver salt of an organic acid may be used in a desired amount, it is preferably used in an amount of 0.1-0.5 g/m2, more preferably of 1-3 g/m2, in terms of silver amount.
The shape of the silver salt of an organic acid that can be used for the present invention is not particularly limited. However, scaly silver salts of an organic acid are preferred for the present invention. Scaly silver salts of an organic acid are herein defined as follows. A sample of a silver salt of an organic acid is observed with an electronic microscope, and grain shapes of the salt are approximated to rectangular parallelepipeds. The three different edges of each rectangular parallelepiped are represented as a, b and c where a is the shortest, c is the longest, and c and b may be the same. From the shorter edges a and b, x is obtained according to the following equation:
x=b/a 
The values of x are obtained for about 200 grains, and an average of them (x (average)) is obtained. Samples that satisfy the requirement of x (average)xe2x89xa71.5 are defined to be scaly. Scaly grains preferably satisfy 30xe2x89xa7x (average)xe2x89xa71.5, more preferably 20xe2x89xa7x (average)xe2x89xa72.0. In this connection, acicular (needle-like) grains satisfy 1xe2x89xa6x (average) less than 1.5.
In scaly grains, it is understood that a corresponds to the thickness of tabular grains of which main planes are defined by the sides of b and c. The average of a is preferably from 0.01 xcexcm to 0.23 xcexcm, more preferably from 0.1 xcexcm to 0.20 xcexcm. The average of c/b is preferably from 1 to 6, more preferably from 1.05 to 4, even more preferably from 1.1 to 3, particularly preferably from 1.1 to 2.
The grain size of the silver salt of an organic acid (volume weight average diameter) can be determined by, for example, irradiating a solid microparticle dispersion of organic acid silver salt in a liquid with a laser ray and determining an autocorrelation function of the fluctuation of the scattered light on the basis of the change in time. The average grain size is preferably 0.05-10.0 xcexcm, more preferably 0.1-5.0 xcexcm, further preferably 0.1-2.0 xcexcm.
The grain size distribution of the non-photosensitive silver salt of an organic acid is preferably monodispersion. The term xe2x80x9cmonodispersionxe2x80x9d as used herein means that the percentage of the value obtained by dividing the standard deviation of the length of the short axis or long axis by the length of the short axis or long axis, respectively, is preferably 100% or less, more preferably 80% or less, further preferably 50% or less.
Another method for determining the dispesibility is a method of obtaining the standard deviation of a volume weight average diameter of the silver salt of an organic acid. The percentage of the value obtained by dividing the standard deviation by the volume weight average diameter (variation coefficient) is preferably 100% or less, more preferably 80% or less, further preferably 50% or less.
As the methods for the production and dispersion of the silver salt of an organic acid used for the present invention, known methods can be used. For example, JP-A-10-62899, EP0803763A1 and EP962812A1 can be referred to.
If a photosensitive silver salt is present during the dispersion of the non-photosensitive silver salt of an organic acid, fog will be increased and sensitivity is markedly lowered. Therefore, it is desirable that the non-photosensitive silver salt of an organic acid is dispersed substantially in the absence of a photosensitive silver salt. In the present invention, the amount of the photosensitive silver salt that may be in the aqueous dispersion of the non-photosensitive silver salt of an organic acid should be 0.1 mole % or less per mole of the silver salt of an organic acid, and the photosensitive silver salt is not added intentionally.
In the present invention, a photosensitive material can be produced by mixing a silver salt of an organic acid aqueous dispersion and a photosensitive silver salt aqueous dispersion. The mixing ratio of the silver salt of an organic acid and the photosensitive silver salt may be selected according to the purpose. However, the ratio of the photosensitive silver salt to the silver salt of an organic acid is preferably from 1 to 30 mole %, more preferably from 3 to 20 mole %, still more preferably from 5 to 15 mole %. In the mixing, two or more kinds of aqueous dispersions of silver salt of an organic acid are preferably mixed with two or more photosensitive silver salt aqueous dispersions in order to control the photographic properties.
The thermally processed image recording material of the present invention contains a reducing agent for silver ions. The reducing agent for silver ions is an arbitrary substance, preferably an organic substance, which reduces silver ions into metal silver. Specific examples of the reducing agent are described in JP-A-11-65021, paragraphs 0043 to 0045 and EP 0803764A1, from page 7, line 34 to page 18, line 12. In the present invention, bisphenol-type reducing agents such as 1,1-bis(2-hydroxy-3,5-dimethylphenyl)-3,5,5-trimethylhexane, 2,2xe2x80x2-methylenebis-(4-methyl-6-tert-butylphenol), 2,2xe2x80x2-methylenebis-(4-methyl-6-tert-butylphenol) are particularly preferred.
The amount of the reducing agent is preferably 0.01-3.0 g/m2, more preferably 0.1-3.0 mmol/m2. The amount is preferably 5-50 mole %, more preferably 10-40 mole %, per 1 mol of silver contained in the layers on the side having the image-forming layer.
The reducing agent may be added to a coating solution in any form such as solution, emulsion dispersion and solid microparticle dispersion so that it could be incorporated into the thermally processed image recording material.
As a well known emulsion dispersion method, there can be mentioned a method of dissolving the reducing agent in an oil such as dibutyl phthalate, tricresyl phosphate, glyceryl triacetate or diethyl phthalate by using an auxiliary solvent such as ethyl acetate or cyclohexanone and mechanically preparing an emulsion dispersion. As the method for preparing solid microparticle dispersion, there can be mentioned a method of dispersing powder of the reducing agent in a suitable solvent such as water by using a ball mill, colloid mill, vibrating ball mill, sand mill, jet mill, roller mill or ultrasonic wave to form solid dispersion. In this operation, a protective colloid (e.g., polyvinyl alcohol), surfactant (e.g., an anionic surfactant such as sodium triisopropylnaphthalenesulfonate (mixture of those having three isopropyl groups on different positions)) and so forth may be used.
The dispersion may contain a preservative (e.g., benzisothiazolinone sodium salt).
The thermally processed image recording material of the present invention preferably contains a photosensitive silver halide. The photosensitive silver halide that can be used for the present invention is not particularly limited as for the halogen composition, and silver chloride, silver chlorobromide, silver bromide, silver iodobromide, silver chloroiodobromide and so forth may be used. The halide composition may have a uniform distribution in the grains, or the compositions may change stepwise or continuously in the grains. Silver halide grains having a core/shell structure may be preferably used. Core/shell grains having preferably a double to quintuple structure, more preferably a double to quadruple structure may be used. A technique for localizing silver bromide on the surface of silver chloride or silver chlorobromide grains may also be preferably used.
For the preparation of the photosensitive silver halide, methods well known in the art, e.g., the methods described in Research Disclosure, No. 17029 (June, 1978) and U.S. Pat. No. 3,700,458, can be used. More specifically, a method can be used which comprises a step of preparing photosensitive silver halide grains by addition of a silver-supplying compound and a halogen-supplying compound to a solution of gelatin or other polymer, and then adding a silver salt of an organic acid to the resulting grains.
As for grain size of the photosensitive silver halide, smaller grains are desirable to prevent cloudiness of the photosensitive material after image formation. Specifically, the grain size may preferably be not greater than 0.20 xcexcm, preferably from 0.01 to 0.15 xcexcm, more preferably from 0.02 to 0.12 xcexcm. The term xe2x80x9cgrain sizexe2x80x9d used herein means a diameter of a sphere having the same volume as the grain where the silver halide grains are regular crystals in cubic or octahedral form and where the silver halide grains are irregular crystals such as spherical or rod-like grains. Where silver halide grains are tabular grains, the term means the diameter of a circle having the same area as a projected area of the main surface of the tabular grain.
Examples of the form of silver halide grains include a cubic form, octahedral form, tabular form, spherical form, rod-like form and potato-like form. In particular, cubic grains are preferred for the present invention. Silver halide grains having round corners are also preferably used in the present invention. Surface index (Miller index) of outer surfaces of the photosensitive silver halide grains is not particularly limited. However, it is desirable that [100] face should be present in a high proportion that can achieve high spectral sensitizing efficiency when a spectral sensitizing dye adsorbed on the grains. The proportion of [100] face may be preferably not lower than 50%, more preferably at least 65%, still more preferably at least 80%. The proportion of Miller index [100] face can be determined using the method described in T. Tani, J. Imaging Sci. , 29, 165 (1985), where the difference in adsorption of a sensitizing dye to [111] face and [100] face is utilized.
The photosensitive silver halide grain preferably contains a metal or metal complex of Group VIII to Group X in the periodic table of elements (including Group I to Group XVIII). The metal or the center metal of the metal complex of Group VIII to X of the periodic table is preferably rhodium, rhenium, ruthenium, osmium or iridium. The metal complex may be used alone, or two or more complexes of the same or different metals may also be used in combination. The metal complex content is preferably from 1xc3x9710xe2x88x929 to 1xc3x9710xe2x88x923 mole per mole of silver. Such metal complexes are described in JP-A-11-65021, paragraphs 0018 to 0024.
In the present invention, an iridium compound is preferably contained in the silver halide grains. Examples of the iridium compound include hexachloroiridium, hexammineiridium, trioxalatoiridium, hexacyanoiridium and pentachloronitrosyl-iridium. The iridium compound is used after dissolving it in water or an appropriate solvent, and a method commonly used for stabilizing the iridium compound solution, more specifically, a method comprising adding an aqueous solution of hydrogen halogenide (e.g., hydrochloric acid, bromic acid, fluoric acid) or halogenated alkali (e.g., KCl, NaCl, KBr, NaBr) may be used. In place of using a water-soluble iridium, separate silver halide grains previously doped with iridium may be added and dissolved at the time of preparation of silver halide. The addition amount of the iridium compound is preferably 1xc3x9710xe2x88x928 to 1xc3x9710xe2x88x923 mole, more preferably 1xc3x9710xe2x88x927 to 5xc3x9710xe2x88x924 mole, per mole of silver halide.
Further, metals and metal complexes that can be contained in the silver halide grains used for the present invention (e.g., [Fe(CN)6]4xe2x88x92), desalting methods and chemical sensitization methods are described in JP-A-11-84574, paragraphs 0046 to 0050 and JP-A-11-65021, paragraphs 0025 to 0031.
The photosensitive silver halide grains are preferably subjected to chemical sensitization by sulfur sensitization, selenium sensitization or tellurium sensitization. Any known compounds are preferably used for such sulfur, selenium or tellurium sensitization, and for example, the compounds described in JP-A-7-128768 are usable for that purpose. In the present invention, especially favorable is tellurium sensitization. Tellurium sensitizers usable herein include, for example, diacyltellurides, bis(oxycarbonyl)tellurides, bis(carbamoyl)tellurides, diacyltellurides, bis(oxycarbonyl)ditellurides, bis (carbamoyl)ditellurides, compounds with P=Te bond, tellurocarboxylates, tellurosulfonates, compounds with Pxe2x80x94Te bond, tellurocarbonyl compounds etc. For these, specifically mentioned are the compounds described in JP-A-11-65021, paragraph 0030. Particularly preferred are those disclosed in JP-A-5-313284 as the compounds of the general formulas (II), (III) and (IV).
The amount of the sulfur, selenium or tellurium sensitizer for use in the present invention varies depending on the type of the silver halide grains to be used, the condition for chemical ripening etc., but may fall generally between 10xe2x88x928 and 10xe2x88x922 mole, preferably between 10xe2x88x927 and 10xe2x88x923 mole or so, per mol of the silver halide. Although the conditions for the chemical sensitization are not particularly limited in the present invention, pH falls between 5 and 8, pAg falls between 6 and 11, preferably between 7 and 10, and temperature falls between 40 and 95xc2x0 C., preferably between 44 and 70xc2x0 C.
In the present invention, the chemical sensitization may be performed at any time so long as it is performed after the formation of the grains and before the coating. It may be performed after desalting and (1) before the spectral sensitization, (2) simultaneously with the spectral sensitization, (3) after the spectral sensitization, (4) immediately before the coating, or the like. It is particularly preferably performed after spectral sensitization.
In the thermally processed image recording material of the present invention, one kind of photosensitive silver halide emulsion may be used or two or more different emulsions (for example, those having different average grain sizes, different halogen compositions, different crystal habits or different chemical sensitization conditions) may be used in combination. By using plural photosensitive silver halides having different sensitivities, contrast can be controlled. Examples of the techniques concerning this respect include those mentioned in JP-A-57-119341, JP-A-53-106125, JP-A-47-3929, JP-A-48-55730, JP-A-46-5187, JP-A-50-73627, JP-A-57-150841 and so forth. Each emulsion may preferably have sensitivity difference of 0.2 log E or higher.
The amount of the photosensitive silver halide is preferably 0.03 to 0.6 g/m2, more preferably 0.05 to 0.4 g/m2, most preferably 0.1 to 0.4 g/m2, as the amount of coated silver per 1 m2 of a photosensitive material. The amount of the photosensitive silver halide per mole of the silver salt of an organic acid is preferably from 0.01 to 0.5 mole, more preferably from 0.02 to 0.3 mole, still more preferably from 0.03 to 0.25 mole.
Methods and conditions for mixing photosensitive silver halide and silver salt of an organic acid, which are prepared separately, are not particularly limited so long as the effect of the present invention can be attained satisfactorily. Examples thereof include, for example, a method of mixing silver halide grains and silver salt of an organic acid after completion of respective preparations by using a high-speed stirring machine, ball mill, sand mill, colloid mill, vibrating mill, homogenizer or the like, or a method of preparing a silver salt of an organic acid by mixing a photosensitive silver halide obtained separately at any time during the preparation of the silver salt of an organic acid.
Preferred addition time point for the silver halide into the coating solution for image-forming layer resides in a period of from 180 minutes before the coating to immediately before the coating, preferably 60 minutes to 10 seconds before the coating. However, the method and conditions for mixing are not particularly limited so long as the effect of the present invention can be attained satisfactorily. Specific examples of the mixing method include a method in which the mixing is performed in a tank designed so that a desired average residence time therein can be obtained, which residence time is calculated from addition flow rate and feeding amount to a coater, a method utilizing a static mixer described in N. Harnby, M. F. Edwards, A. W. Nienow, xe2x80x9cEkitai Kongo Gijutsu (Techniques for Mixing Liquids)xe2x80x9d, translated by Koji Takahashi, Chapter 8, Nikkan Kogyo Shinbunsha, 1989 and so forth.
As a sensitizing dye that can be used for the present invention, there can be advantageously selected those sensitizing dyes which can spectrally sensitize silver halide grains within a desired wavelength range after they are adsorbed by the silver halide grains and have spectral sensitivity suitable for spectral characteristics of the light source to be used for exposure. Such sensitizing dyes and addition methods therefor are described in JP-A-11-65021, paragraphs 0103 to 0109 and EP 0803764A1, page 19, line 38 to page 20, line 35, and there can be mentioned the compounds of formula (II) described in JP-A-10-186572. In the present invention, the sensitizing dye is preferably added to the silver halide emulsion during the period after the desalting step and before the coating step, more preferably during the period after the desalting step and before the start of the chemical ripening.
In the thermally processed image recording material of the present invention, the phenol derivatives represented by the formula (A) mentioned in Japanese Patent Application No. 11-73951 are preferably used as a development accelerator.
In the thermally processed image recording material of the present invention, an image-hardening agent, that is, so-called nucleating agent, can be used in order to obtain high contrast images. While type of the nucleating agent that can be used in the present invention is not particularly limited, examples thereof include all of the hydrazine derivatives described in JP-A-10-10672, JP-A-10-161270, JP-A-10-62898, JP-A-9-304870, JP-A-9-304872, JP-A-9-304871, JP-A-10-31282, U.S. Pat. No. 5,496,695 and EP741320A. Further, the hydrazine derivatives represented by the formula (H) mentioned in Japanese Patent Application No. 11-87297, specifically, the hydrazine derivatives mentioned in Tables 1-4 of the same, can also be preferably used. Furthermore, the substituted alkene derivatives, substituted isoxazole derivatives and acetal compounds represented by the formulas (1) to (3) mentioned in Japanese Patent Application No. 11-87297, more preferably the cyclic compounds represented by the formula (A) or (B) mentioned in the same, specifically Compounds 1-72 mentioned in Chem. 8 to Chem. 12 of the same, can also be used. In addition to these compounds, any of the compounds described in U.S. Pat. Nos. 5,545,515, 5,635,339, 5,654,130 and 5,686,228, International Patent Publication WO97/34196, and JP-A-11-119372, JP-A-11-109546, JP-A-11-119373, JP-A-11-133546, JP-A-11-95365 and JP-A-11-95366 may also be used. Two or more of these nucleating agents may be used in combination.
The amount of the nucleating agent is 1xc3x9710xe2x88x926 mole to 1 mole, more preferably from 1xc3x9710xe2x88x925 mole to 5xc3x9710xe2x88x921 mole, further preferably from 2xc3x9710xe2x88x925 mole to 2xc3x9710xe2x88x921 mole, per mol of silver.
While the nucleating agent may be added to any layer on the image-forming layer side including the image-forming layer and the other layers, it is preferably added to the image-forming layer or a layer adjacent thereto.
The nucleating agent may be used after being dissolved in an appropriate organic solvent such as an alcohol (e.g., methanol, ethanol, propanol, fluorinated alcohol), a ketone (e.g., acetone, methyl ethyl ketone), dimethylformamide, dimethyl sulfoxide or methyl cellosolve. Further, it may also be used as an emulsion dispersion mechanically prepared according to an already well known emulsion dispersion method by using an oil such as dibutyl phthalate, tricresyl phosphate, glyceryl triacetate or diethyl phthalate, ethyl acetate or cyclohexanone as an auxiliary solvent for dissolution. Alternatively, the nucleating agent may be used by dispersing powder of the nucleating agent in a suitable solvent such as water using a ball mill, a colloid mill, or by means of ultrasonic wave according to a known method for solid dispersion.
In the present invention, a contrast accelerator may be used in combination with the above-described nucleating agent for the formation of an ultrahigh contrast image. For example, amine compounds described in U.S. Pat. No. 5,545,505, specifically, AM-1 to AM-5; hydroxamic acids described in U.S. Pat. No. 5,545,507, specifically, HA-1 to HA-11; acrylonitriles described in U.S. Pat. No. 5,545,507, specifically, CN-1 to CN-13; hydrazine compounds described in U.S. Pat. No. 5,558,983, specifically, CA-1 to CA-6; and onium salts described in JP-A-9-297368, specifically, A-1 to A-42, B-1 to B-27 and C-1 to C-14 may be used.
When a nucleating agent is used in the thermally processed image recording material the present invention, an acid formed by hydration of diphosphorus pentoxide or a salt thereof is preferably used together with the nucleating agent. Examples of the acid formed by hydration of diphosphorus pentoxide or a salt thereof include metaphosphoric acid (salt), pyrophosphoric acid (salt), orthophosphoric acid (salt) triphosphoric acid (salt), tetraphosphoric acid (salt), hexametaphosphoric acid (salt) and so forth. Particularly preferably used acids formed by hydration of diphosphorus pentoxide or salts thereof are orthophosphoric acid (salt) and hexametaphosphoric acid (salt). Specific examples of the salt are sodium orthophosphate, sodium dihydrogenorthophosphate, sodium hexametaphosphate, ammonium hexametaphosphate and so forth.
The acid formed by hydration of diphosphorus pentoxide or a salt thereof may be used in a desired amount depending on the desired performance including sensitivity and fog. However, it can preferably be used in an amount of 0.1-500 mg/m2, more preferably 0.5-100 mg/m2, in terms of coating amount per 1 m2 of the thermally processed image recording material.
The acid formed by hydration of diphosphorus pentoxide or a salt thereof that can be preferably used in the present invention is added to the image-forming layer or a binder layer adjacent thereto in order to obtain the desired effect with a small amount of the acid or a salt thereof.
Formic acid and formic acid salts serve as a strongly fogging substance in a thermally processed image recording material containing a photosensitive silver halide and a binder. In the present invention, the thermally processed image recording material preferably contains formic acid or a formic acid salt on the side having the image-forming layer containing a photosensitive silver halide in an amount of 5 mmol or less, more preferably 1 mmol or less, per 1 mole of silver.
As antifoggants, stabilizers and stabilizer precursors that can be used for the present invention, there can be mentioned, for example, those mentioned in JP-A-10-62899, paragraph 0070 and EP 0803764A1, from page 20, line 57 to page 21, line 7. Antifoggants preferably used in the present invention are organic polyhalogenated compounds. Examples thereof include those mentioned in JP-A-11-65021, paragraphs 0111-0112. In particular, the polyhalogenated compounds represented by the general formula (II) mentioned in JP-A-10-339934 (specific examples are tribromomethylnaphthyl-sulfone, tribromomethylphenylsulfone, tribromemethyl(4-(2,4,6-trimethylphenylsulfonyl)phenyl)sulfone etc.) are preferred.
The antifoggant can be added to the thermally processed image recording material, for example, in the same manner as that for the reducing agent described above. The polyhalogenated compound is also preferably added as solid microparticle dispersion.
Other examples of the antifoggant include the mercury(II) salts described in JP-A-11-65021, paragraph 0113, and the benzoic acids described in the same, paragraph 0114.
The thermally processed image recording material of the present invention may contain an azolium salt as the antifoggant. Examples of the azolium salt include, for example, the compounds of the general formula (XI) described in JP-A-59-193447, the compounds described in JP-B-55-12581 and the compounds of the general formula (II) described in JP-A-60-153039. The azolium salt may be added to any site of the thermally processed image recording material, but is preferably added to a layer on the image-forming layer side, more preferably to the image-forming layer. The azolium salt may be added at any time during the preparation of the coating solution. When the azolium salt is added to the image-forming layer, it may be added at any time during the period of from the preparation of the silver salt of an organic acid to the preparation of the coating solution. However, the azolium salt is preferably added during the period after the preparation of the silver salt of an organic acid and immediately before the coating. The azolium salt may be added in any form such as powder, solution and microparticle dispersion. It may also be added as a solution that also contains other additives such as sensitizing dye, reducing agent and toning agent. In the present invention, the amount of the azolium salt to be added is not particularly limited, but it is preferably 1xc3x9710xe2x88x926 mole to 2 moles, more preferably 1xc3x9710xe2x88x923 mole to 0.5 mole, per mole of silver.
The thermally processed image recording material of the invention may optionally contain any of mercapto compounds, disulfide compounds and thione compounds in order to control development by retarding or accelerating it, or enhance spectral sensitization efficiency, or improve storage stability before and after development. Examples of those compounds include, for example, those described in JP-A-10-62899, paragraphs 0067 to 0069, those of the formula (I) mentioned in JP-A-10-186572 and those described in EP 0803764A1, page 20, lines 36 to 56. Among these, preferred are mercapto-substituted heteroaromatic compounds.
The thermally processed image recording material of the present invention is preferably added with a toning agent. Examples of the toning agent are mentioned in JP-A-10-62899, paragraphs 0054 to 0055 and EP 0803764A1, page 21, lines 23 to 48. Preferred are phthalazinone, phthalazinone derivatives (e.g., 4-(1-naphthyl)phthalazinone, 6-chlorophthalazinone, 5,7-dimethoxyphthalazinone, 2,3-dihydro-1,4-phthalazinone and other derivatives) and metal salts thereof; combinations of phthalazinones and phthalic acid or derivatives thereof (e.g., phthalic acid, 4-methylphthalic acid, 4-nitrophthalic acid, tetrachlorophthalic anhydride etc.); phthalazines including phthalazine and phthalazine derivatives (e.g., 4-(1-naphthyl)phthalazine, 6-isopropylphthalazine, 6-tert-butylphthalazine, 6-chlorophthalazine, 5,7-dimethoxyphthalazine, 2,3-dihydrophthalazine and other derivatives) and metal salts thereof; combinations of phthalazines and phthalic acid or derivatives thereof (e.g., phthalic acid, 4-methylphthalic acid, 4-nitrophthalic acid, tetrachlorophthalic anhydride etc.). Particularly preferred are combinations of phthalazines and phthalic acid derivatives.
Plasticizers and lubricants that can be used for the image-forming layer of the thermally processed image recording material of the present invention are described in JP-A-11-65021, paragraph 0117.
In the present invention, for the image-forming layer, various types of dyes and pigments may be used to improve color tone, to prevent interference fringes generated during laser exposure, and to prevent irradiation. These techniques are detailed in International Patent Publication WO98/36322. Preferred dyes and pigments include, for example, anthraquinone dyes, azomethine dyes, indoaniline dyes, azo dyes, indanthrone pigments of anthraquinone type (e.g., C.I. Pigment Blue 60 etc.), phthalocyanine pigments (e.g., copper phthalocyanines such as C.I. Pigment Blue 15; metal-free phthalocyanines such as C.I. Pigment Blue 16), triarylcarbonyl pigments of printing lake pigment type, indigo, inorganic pigments (e.g., ultramarine, cobalt blue etc.). Any methods are employed to add these dyes and pigments such as addition as a solution, emulsion, or dispersion of solid microparticles, or addition of a polymer mordant mordanted with these. The amount of these compounds to be used may vary depending on intended absorbance. In general, the compounds may preferably be used in an amount of 1 xcexcg to 1 g per m2 of the thermally processed image recording material.
The image-forming layer of the thermally processed image recording material of the present invention may contain a polymer such as latex polymer not according to the present invention, gelatin, polyvinyl alcohol, methylcellulose and hydroxypropylcellulose, as required. The amount of the hydrophilic polymer is preferably 30 weight % or less, more preferably 20 weight % or less, of the total binder in the image-forming layer.
In the present invention, an antihalation layer may be provided in a distant position from a light source relative to the image-forming layer. The antihalation layer is described in JP-A-11-65021, paragraphs 0123 to 0124.
In the thermally processed image recording material of the present invention, a decoloring dye and a base precursor can be added to a non-photosensitive layer of the thermally processed image recording material so that the non-photosensitive layer can function as a filter layer or an antihalation layer. Thermally processed image recording materials generally have non-photosensitive layers in addition to the photosensitive layers. Depending on their positions, the non-photosensitive layers are classified into (1) a surface protective layer to be provided on a photosensitive layer (the distant side from the support); (2) an intermediate layer to be provided between two or more of photosensitive layers or between a photosensitive layer and a surface protective layer; (3) an undercoat layer to be provided between a photosensitive layer and a support; (4) a back layer to be provided on a side opposite to the photosensitive layer. The filter layer is provided in the photosensitive material as the layer (1) or (2). The antihalation layer is provided in the photosensitive material as the layer (3) or (4).
The decoloring dye and the base precursor are preferably added to the same non-photosensitive layer. However, they may also be added separately to adjacent two non-photosensitive layers. If desired, a barrier layer may be provided between the two non-photosensitive layers.
As methods to add a decoloring dye to a non-photosensitive layer, a method may be employed which comprises step of adding a solution, emulsion, solid microparticle dispersion of the dye, or adding the dye impregnated in a polymer to a coating solution for the non-photosensitive layer. The dye may also be added to the non-photosensitive layer by using a polymer mordant. These methods for addition are the same as those generally employed for the addition of dyes to ordinary thermally processed image recording materials. Polymer latexes used for preparation of the dye impregnated in a polymer are described in U.S. Pat. No. 4,199,363, German Patent Laid-open Nos. 25,141,274, 2,541,230, EP029104A and JP-B-53-41091. A method for emulsification by adding a dye to a solution in which a polymer is dissolved is described in International Patent Publication WO88/00723.
The amount of the decoloring dye may be determined depending on purpose of the use of the dye. In general, the dye is used in an amount to give an optical density (absorbance) of larger than 0.1 measured at an intended wavelength. The optical density is preferably 0.2 to 2. The amount of the dye to give such optical density may be generally from about 0.001 to about 1 g/m2, particularly preferably from about 0.01 to about 0.2 g/m2.
Decoloring of dyes in that manner can lower optical density of the material to 0.1 or less. Two or more different decoloring dyes may be used in the thermodecoloring type recording materials or photothermographic materials. Similarly, two or more different base precursors may be used in combination.
The thermally processed image recording material of the present invention may further contain antioxidant, stabilizer, plasticizer, UV absorber, coating aid, crosslinking agent and so forth. These various additives are added to the photosensitive layer or the non-photosensitive layer. As for these, WO98/36322, EP803764A1, JP-A-10-186567, JP-A-10-18568 and so forth can be referred to.
Supports that can be used in the present invention are described in JP-A-11-65021, paragraph 0134; usable surfactants are described in the same, paragraph 0133; usable solvents are described in the same, paragraph 0133; usable antistatic and electroconductive layers are described in the same, paragraph 0135; and usable methods for forming color images are described in the same, paragraph 0136.
Preferably used as a transparent support is a polyester film, in particular, polyethylene terephthalate film, subjected to a heat treatment in a temperature range of 130-185xc2x0 C. in order to relax the internal distortion formed in the film during the biaxial stretching so that thermal shrinkage distortion occurring during the heat development could be eliminated. When the thermally processed image recording material is for medical use, the transparent support may be colored with blue dyes (e.g., Dye-1 described in Examples of JP-A-8-240877), or may be colorless. For the support, techniques for undercoating described in JP-A-11-84574 (utilizing water-soluble polyester), JP-A-10-186565 (utilizing styrene/butadiene copolymer), Japanese Patent Application No. 11-106881, paragraphs 0063-0080 (utilizing vinylidene chloride copolymer) and so forth are preferably used. As for antistatic layers and undercoating, techniques disclosed in JP-A-56-143430, JP-A-56-143431, JP-A-58-62646, JP-A-56-120519, JP-A-11-84573, paragraphs 0040-0051, U.S. Pat. No. 5,575,957, JP-A-11-223898, paragraphs 0078-0084 and so forth can also be used.
The thermally processed image recording material of the present invention is constituted by one or more layers on the support. When it is constituted with a monolayer, the layer must contain a silver salt of an organic acid, developing agent, and binder as well as desired additional materials such as silver halide, toning agent, coating aid and other auxiliary agents. When the layer is bilayer, the first image-forming layer (in general, the layer adjacent to the support) may contain a silver salt of an organic acid and silver halide, and the second layer or the both layers may contain several other ingredients. Another type of bilayer structure is also employable in which one layer is a single image-forming layer containing all necessary ingredients and the other layer is a protective top coat layer. Multicolor thermally processed image recording material may contain these two layers for each color, or may contain all necessary ingredients in a single layer as described in U.S. Pat. No. 4,708,928. As for multicolor thermally processed image recording material containing multiple dyes, each image-forming layer is kept individually by using a functional or non-functional barrier layer between the adjacent photosensitive layers as described in U.S. Pat. No. 4,460,681.
The thermally processed image recording material of the present invention is preferably a so-called single-sided photosensitive material comprising at least one photosensitive layer containing a silver halide emulsion on one side of support, and a back layer on the other side.
The thermally processed image recording material of the invention is preferably of a monosheet type. The monosheet type does not use any additional sheets such as image receiving materials, but can form images directly on the material itself.
The temperature for preparation of the coating solution for the image-forming layer may preferably be 30xc2x0 C. to 65xc2x0 C., more preferably 35xc2x0 C. to 60xc2x0 C., most preferably 35xc2x0 C. to 55xc2x0 C. The temperature of the coating solution for the image-forming layer immediately after the addition of the polymer latex may preferably be kept at 30xc2x0 C. to 65xc2x0 C. A reducing agent and a silver salt of an organic acid may preferably be mixed before the addition of polymer latex.
The fluid containing silver salt of organic acid or coating solution for the thermally image-forming layer is preferably a so-called thixotropic flow. Thixotropy means that viscosity of a fluid lowers with increase of shear rate. Any apparatus may be used for measurement of viscosity. For example, RFS Fluid Spectrometer from Rheometrics Far East Co., as Ltd. is preferably used, and the measurement is performed at 25xc2x0 C. Viscosity of the fluid containing silver salt of organic acid or coating solution for the thermally image-forming layer is preferably 400 mPaxc2x7s to 100,000 mPaxc2x7s, more preferably 500 mPaxc2x7s to 20,000 mPaxc2x7s, at a shear rate of 0.1 secxe2x88x921. The viscosity is preferably 1 mPaxc2x7s to 200 mPaxc2x7s, more preferably 5 mPaxc2x7s to 80 mPaxc2x7s, at a shear rate of 1000 secxe2x88x921.
Various systems exhibiting thixotropic property are known and, for example, described in xe2x80x9cKoza Rheology (Lecture on Rheology)xe2x80x9d, Kobunshi Kanko Kai; Muroi and Morino, xe2x80x9cPolymer Latexxe2x80x9d, Kobunshi Knako Kai and so forth. A fluid is required to contain a large amount of fine solid microparticles to exhibit thixotropic property. For enhancing thixotropic property, it is effective that the fluid is added with a viscosity-increasing linear polymer, or fine solid microparticles to be contained have anisotropic shapes and an increased aspect ratio. Use of an alkaline viscosity-increasing agent or a surfactant is also effective for that purpose.
In the present invention, the surface protective layer may contain a matting agent for improving the transferability of the material. The matting agent may also be contained in a layer functioning as a surface protective layer, or in a layer near the outer surface. The matting agent is preferably contained in a surface protective layer and/or a layer functioning as a surface protective layer.
Matting agents are described in JP-A-11-65021, paragraphs 0126 to 0127. The matting agent is added in an amount of preferably 1 to 400 mg/m 2, more preferably 5 to 300 mg/m2, as the amount per 1 m2 of the recording material.
While the matting degree of the surface of the image-forming layer side is not particularly limited so long as the material is free from stardust defects, Beck""s smoothness of the surface is preferably 30 seconds to 2000 seconds, more preferably 40 seconds to 1500 seconds.
The matting degree of the back surface is preferably falls 10 seconds to 1200 seconds, more preferably 20 seconds to 800 seconds, further preferably 40 seconds to 500 seconds as shown by the Beck""s smoothness.
The back layers that can be used for the present invention are described in, for example, JP-A-11-65021, paragraphs 0128 to 0130.
In the present invention, a hardening agent may be added to the image-forming layer, protective layer, back layer, and other layers. As for the hardening agent, various methods are described in T. H. James, xe2x80x9cTHE THEORY OF THE PHOTOGRAPHIC PROCESS, FOURTH EDITIONxe2x80x9d, Macmillan Publishing Co., Inc., 1977, pp. 77-87. Polyvalent metal ions described on page 78 of the above article, polyisocyanates described in U.S. Pat. No. 4,281,060 and JP-A-6-208193, epoxy compounds described in U.S. Pat. No. 4,791,042, vinylsulfone compounds described in JP-A-62-89048 and so forth may preferably be used.
The hardening agent is added to coating solutions for protective layers as a solution. Preferred addition time of the solution resides in a period of from 180 minutes before the coating to just before the coating, preferably 60 minutes to 10 seconds before the coating. The method and conditions for mixing are not particularly limited so long as the effect of the present invention can be obtained satisfactorily. Specific examples of the mixing method include a method in which a mixing is performed in a tank designed so as to obtain a desired average residence time which is calculated from addition flow rate and feeding amount to a coater, a method utilizing a static mixer described in N. Harnby, M. F. Edwards, A. W. Nienow, xe2x80x9cEkitai Kongo Gijutsu (Techniques for Mixing Liquids)xe2x80x9d, translated by Koji Takahashi, Chapter 8, Nikkan Kogyo Shinbunsha, 1989 and so forth.
The thermally processed image recording material of the present invention may be provided with a surface protective layer, for example, to prevent adhesion of the image-forming layer. The surface protective layer is described in, for example, JP-A-11-65021, paragraphs 0119 to 0120.
In the present invention, the binder forming the surface protective layer is not particularly limited so long as it is a usual polymer material having film-forming property, and a water-soluble polymer or oil-soluble polymer in any form selected from aqueous solution, aqueous dispersion, solution in an organic solvent and so forth can be used. Examples of usable materials are also described in JP-A-11-65021. Preferred examples of water-soluble polymers include gelatin, polyvinyl alcohol (PVA) and so forth. Examples of polyvinyl alcohol include, for example, completely saponified PVA (e.g., PVA-105, available from Kraray Co., Ltd.), partially saponified PVA (e.g., PVA-205, available from Kraray Co., Ltd.), denatured polyvinyl alcohol (e.g., PVA-102, MP-203 available from Kraray Co., Ltd.) and so forth.
The application amount of the water-soluble binder for one surface protective layer is preferably 0.3 to 4.0 g/m2, more preferably 0.3 to 2.0 g/m2.
When the thermally processed image recording material of the present invention is used for, in particular, printing use is which dimensional change is critical, polymer latex is preferably used also in a protective layer or a back layer. Such latex is described in xe2x80x9cGosei Jushi Emulsion (Synthetic Resin Emulsion)xe2x80x9d, compiledby Taira Okuda and Hiroshi Inagaki, issued by Kobunshi Kanko Kai (1978); xe2x80x9cGosei Latex no Oyo (Application of Synthetic Latex)xe2x80x9d, compiled by Takaaki Sugimura, Yasuo Kataoka, Souichi Suzuki and Keishi Kasahara, issued by Kobunshi Kanko Kai (1993); Soichi Muroi, xe2x80x9cGosei Latex no Kagaku (Chemistry of Synthetic Latex)xe2x80x9d, Kobunshi Kanko Kai (1970) and so forth. Specific example thereof include latex of methyl methacrylate (33.5 weight %)/ethyl acrylate (50 weight %)/methacrylic acid (16.5 weight %) copolymer, latex of methyl methacrylate (47.5 weight %)/butadiene (47.5 weight %)/itaconic acid (5 weight %) copolymer, latex of ethyl acrylate/methacrylic acid copolymer, latex of methyl methacrylate (58.9 weight %)/2-ethylhexyl acrylate (25.4 weight %)/styrene (8.6 weight %)/2-hydroxyethyl methacrylate (5.1 weight %)/acrylic acid (2.0 weight %) copolymer and so forth. As for the binder of the protective layer, there may be used the combination of polymer latex disclosed in Japanese Patent Application No. 11-6872, and techniques disclosed in Japanese Patent Application No. 11-143058, paragraphs 0021-0025, Japanese Patent Application No. 11-6872, paragraphs 0027-0028 and Japanese Patent Application No. 11-199626, paragraphs 0023-0041.
The coating methods for coating solutions of the layers used in the production of the thermally processed image recording material of the present invention are not particularly limited, and any coating method can be used. Specific examples thereof include various types of coating techniques, for example, extrusion coating, slide coating, curtain coating, dip coating, knife coating, flow coating, extrusion coating utilizing a hopper of the type described in U.S. Pat. No. 2,681,294 and so forth. Preferably used are extrusion coating and slide coating described in Stephen F. Kistler, Petert M. Schweizer, xe2x80x9cLIQUID FILM COATINGxe2x80x9d, published by CHAPMAN and HALL Co., Ltd., 1997, pp. 399-536, and particularly preferably used is the slide coating. An example of the shape of slide coater used for the slide coating is shown in FIG. 11b, 1, on page 427 of the aforementioned reference. If desired, two or more layers may be coated simultaneously, for example, according to the methods described from page 399 to page 536 of the aforementioned reference, or the methods described in U.S. Pat. No. 2,761,791 and British Patent No. 837,095.
The thermally processed image recording material of the present invention preferably has a film surface pH of 6.0 or less, more preferably 5.5 or less before heat development. While the lower limit is not particularly limited, it is normally around 3. For controlling the film surface pH, an organic acid such as phthalic acid derivatives or a nonvolatile acid such as sulfuric acid, and a volatile base such as ammonia are preferably used to lower the film surface pH. In particular, ammonia is preferred to achieve a low film surface pH, because it is highly volatile and therefore it can be removed before coating or heat development. A method for measuring the film surface pH is described in Japanese Patent Application No. 11-87297, paragraph 0123.
Other techniques that can be used for the production of the thermally processed image recording material of the present invention are also described in EP803764A1, EP883022A1, WO98/36322, JP-A-56-62648, JP-A-58-62644, JP-A-9-281637, JP-A-9-297367, JP-A-9-304869, JP-A-9-311405, JP-A-9-329865, JP-A-10-10669, JP-A-10-62899, JP-A-10-69023, JP-A-10-186568, JP-A-10-90823, JP-A-10-171063, JP-A-10-186565, JP-A-10-186567, JP-A-10-186569, JP-A-10-186570, JP-A-10-186571, JP-A-10-186572, JP-A-10-197974, JP-A-10-197982, JP-A-10-197983, JP-A-10-197985, JP-A-10-197986, JP-A-10-197987, JP-A-10-207001, JP-A-10-207004, JP-A-10-221807, JP-A-10-282601, JP-A-10-288823, JP-A-10-288824, JP-A-10-307365, JP-A-10-312038, JP-A-10-339934, JP-A-11-7100, JP-A-11-15105, JP-A-11-24200, JP-A-11-24201, JP-A-11-30832, JP-A-11-84574, JP-A-11-65021, JP-A-11-125880, JP-A-11-129629, JP-A-11-133536, JP-A-11-133537, JP-A-11-133538, JP-A-11-133539, JP-A-11-133542 and JP-A-11-133543.
The thermally processed image recording material of the present invention may be developed in any manner. Usually, an imagewise exposed thermally processed image recording material is developed by heating. The development temperature is preferably 80xc2x0 C. to 250xc2x0 C., more preferably 100xc2x0 C. to 140xc2x0 C. The development time is preferably 1 to 180 seconds, more preferably 10 to 90 seconds, particularly preferably 10 to 40 seconds.
For thermal development for the material, preferred is a plate heater system. For heat development by the plate heater system, the method described in JP-A-11-133572 is preferred. The plate heater system described in this reference is a heat development apparatus wherein a thermally processed image recording material on which a latent image is formed is brought into contact with heating means in a heat development section to obtain a visible image. In this apparatus, the heating means comprises a plate heater, and a plurality of presser rollers are disposed facing to one surface of the plate heater. Heat development of the thermally processed image recording material is attained by passing the material between the presser rollers and the plate heater. The plate heater is preferably sectioned into 2 to 6 stages, and the temperature of the top stage is preferably kept lower by 1 to 10xc2x0 C. or so than that of the others. Such a method is also described in JP-A-54-30032. Such a plate heater system can remove moisture and organic solvent contained in the thermally processed image recording material out of the material, and prevent deformation of the support of the thermally processed image recording material by rapidly heating the material.
The thermally processed image recording material of the present invention can be exposed in any manner. As light source of exposure, laser rays are preferred. As the laser used in the present invention, gas lasers (Ar+, Hexe2x80x94Ne), YAG lasers, dye lasers, semiconductor lasers and so forth are preferred. A combination of semiconductor laser and second harmonic generating device may also be used. Preferred are gas or semiconductor lasers for red to infrared emission.
Single mode lasers can be used for the laser rays, and the technique disclosed in JP-A-11-65021, paragraph 0140, can be used.
The laser output is preferably at least 1 mW, more preferably at least 10 mW. Even more preferred is high output of at least 40 mW. If desired, a plurality of lasers may be multiplexed. The diameter of laser ray may be in the range of 30 and 200 xcexcm or so in terms of 1/e2 spot size of a Gaussian beam.
As an example of laser imager provided with a light exposure section and heat development section, Fuji Medical Dry Imager FM-DP L can be mentioned.
FM-DP L is explained in Fuji Medical Review, No. 8, pages 39-55, and those techniques can of course be used in laser imagers for the thermally processed image recording material of the present invention.
The thermally processed image recording material of the present invention forms a monochromatic image based on silver image, and is preferably used as a thermally processed image recording material for use in medical diagnosis, industrial photography, printing and COM. In such applications, the monochromatic images formed can of course be duplicated on duplicating films, MI-Dup, from Fuji Photo Film for medical diagnosis; and for printing, the images can be used as the mask for forming images on films for reverse images such as DO-175 and PDO-100 from Fuji Photo Film, or on offset printing plates.